Sewage tank system and method of construction

ABSTRACT

A sewage collection and separation tank (10) and method of construction is described. The sewage tank is built on a prepared earthen site (21) and is comprised of a tank floor (11) constructed from multiple wedge shaped concrete floor sections (13, 15, 17 and 19) that encase a first elastomeric gasket (37) mounted around the perimeter of a centrally located sump pump pit (23). A second elastomeric gasket (41) is mounted in a side (13c) of the first section so that half of the second gasket remains exposed. The tank floor is completed when the fourth section is poured. By the time the fourth section of the tank floor is poured, the first section has cured to the point that the first section will not seal against the wet concrete of the fourth section. However, a side (19e) of the fourth section, adjacent to the first section, encases the exposed half of the second gasket. This provides a liquid impervious seal between the adjacent first and fourth sections. Without the second gasket, the first and fourth sections would not be capable of sealing against each other. The sewage tank is completed by continual interlocking sidewall panels (25) that are mounted around the perimeter of the tank floor and by interlocking roof panels (not shown) mounted on the wall panels and supported by columns (not shown).

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a sewage collection and separation tanksystem and method of construction Because sewage tanks are usually largein area, the sewage tank floor is preferably built from concretesections, poured radially around a centrally located sump pump pit. Thesections are usually wedge shaped or pie shaped and comprised of a lowerface adjacent to an earthen pit or excavation, an upper face parallel tothe lower face and first and second sides between the faces. To create awater tight, leak-proof concrete floor for the sewage tank system, it isnecessary to ensure that the next section is poured abutting against awet side of the previous section. When pouring a substantial area ofconcrete, like a sewage tank floor, it is extremely difficult to getadjoining sides of the first and last sections of the tank floor to sealalong their common seam. The first side of the first section will almostalways be too dry by the time the second side of the last section ispoured to provide a water tight seam between the first and lastsections. This can allow fluid held in the tank to leak through the seamand result in pollution which can be economically and environmentallydamaging.

As a solution to this problem a first elastomeric gasket is mounted in agroove around the perimeter of the sump pump pit wall. This first gasketis encased in concrete as the sections of the sewage tank floor arepoured radially around the sump pump pit and provides an imperviousliquid seal between the floor of the sewage tank and the sump pump pit.

A second elastomeric gasket, preferably made of rubber, is mounted in agroove in the first side of the first section of the sewage tank floorso that half of the gasket projects outside of the groove. Regardlesswhether the concrete at the first side has set-up or dried by the timethe last section is poured, the second side of the last section willencase the exposed half of the second gasket, forming a liquid tightseal between the first and last sections. The second gasket thus acts asan impervious member along the seam between the first and last sectionsand prevents the seepage of liquids held in the sewage tank into theground below the tank.

Preformed wall panels are mounted in a channel formed around an outerperiphery of the tank floor. The wall panels are preferably sealed tothe tank floor by a third elastomeric gasket or with a bitumasticcompound poured over a non-shrink grout in the channel around the outerperiphery of the tank floor. The seal between the wall panels and thetank floor in the channel can also be provided by the third elastomericgasket in conjunction with a bitumastic compound. The third gasket abutsagainst the second gasket to provide a seal between the wall panels andthe first and last sections of the tank floor. Finally, adjoining wallpanels are joined to each other with a joint made of a tongue and agroove provided in the adjoining edges of the wall panels. The tongueand groove joint can be further sealed with a fourth elastomeric gasket,or a sealing compound like tar or an asphalt based compound such as abitumastic coating over a non-shrink grout or both the elastomericgasket and the bitumastic coating in conjunction with each other.

(2) Prior Art

The prior art has described various types of concrete holding tanks andconcrete pools for holding liquids. However, none of the prior art showsa sewage tank system and method of construction that uses an elastomericgasket encased between a dry side and a wet side of adjoining pouredconcrete sections of the sewage tank floor to provide a seal along theseam between the adjoining sections.

The prior art holding tanks and pools are typically built having aunitary concrete floor with side walls made of concrete panels. Theconcrete panels are mounted side-by-side in a groove formed in theconcrete floor. The concrete panels are then sealed to the floor bycast-in-place concrete beams. For added sealing, a water stop sealingmaterial is preferably encased between the concrete floor and theconcrete panels and between the side-by-side concrete panels by thecast-in-place concrete. This prior art is illustrated by U.S. Pat. Nos.Re 29,777 to Crowley and 4,126,976 to Crowley.

U.S Pat. Nos. 3,642,138 to Sheda and 4,550,538 to Blakeway areillustrative of liquid holding tanks that use a sealing strip between ametal surface and a concrete foundation or between two metal surfaces toprovide a water tight seal. The sealing strip is usually made of anelastomeric material such as a rubber, although tar and oakum also workwell.

OBJECTS

It is therefore an object of the present invention to provide a sewagecollection and separation tank system comprised of a plurality ofconcrete tank floor sections poured radially around the perimeter of acentrally located sump pump pit and having an elastomeric gasketextending radially from the sump pump pit between abutting sides of twoadjoining sections. The gasket provides a liquid tight seal between theadjoining sections. Further, it is an object of the present invention toprovide a method constructing a sewage collection and separation tanksystem comprised of a plurality of poured concrete tank floor sectionsfanning radially from a centrally located sump pump pit. Theconstruction method uses an elastomeric gasket that is encased by afirst side of a first section and a second side of a last section toprovide a liquid impervious seal along the seam between the first andlast sections.

Further, it is an object of the present invention to provide a sewagecollection and separation tank system wherein an elastomeric gasket isencased along a seam between a dried concrete member and a wet concretemember to provide a liquid impervious seal between the adjoining wet anddry concrete members. Furthermore, it is an object of the presentinvention to provide a poured concrete sewage collection and separationtank system mounted in a earthen pit that does not allow seepage ofliquids held in the tank through seams between adjoining concretemembers comprising the tank. These and other objects will becomeincreasingly apparent by reference to the following descriptions and tothe drawings.

IN THE DRAWINGS

FIG. 1 is a plan view of the construction of a concrete sewagecollection and separation tank 10 showing a sump pump pit 23 mounted ina sump pump pit excavation 27 with a first concrete section 13 of thesewage tank floor 11 extending from the sump pump pit 23.

FIG. 2 is a plan view of the construction of the sewage collection andseparation tank 10 showing the progression of a second concrete section15 of the sewage tank floor 11 poured adjacent to the first section 13and extending radially around the perimeter of the sump pump pit 23.

FIG. 3 is a plan view of the construction of the sewage collection andseparation tank showing the progression of a third concrete section 17of the sewage tank floor 11 poured adjacent to the second section 15 andextending radially around the circumference of the sump pump pit 23.

FIG. 4 is a plan view of the construction of the sewage collection andseparation tank showing the progression of a fourth section 19 of thesewage tank floor 11 extending from the sump pump pit 23 between thefirst and third sections 13 and 17 of the sewage tank floor 11.

FIG. 5 is a front cross-sectioned view along line 5--5 of FIG. 4 showinga sealing gasket 41 encased between the first section 13 and the fourthsection 19 of the sewage tank floor 11.

FIG. 6 is a front cross-sectioned view along line 6--6 of FIG. 4 showinga sealing gasket 37 mounted in a groove 35 provided around the perimeterof the sump pump pit 23 and encased by the first 13 and the third 17sections of the sewage tank floor 11.

FIG. 7 is a plan perspective view showing the earthen site 21 for thesewage tank 10 with a sump pump excavation pit 27 and a plurality offootings 29 dug in the earthen site 21 and with a shoulder 31 contouredaround the perimeter of the earthen site 21.

FIG. 8 is a cross-sectioned view along lines 8-8 of FIG. 4 showing theslope of the second and fourth sections 15 and 19 extending from thesump pump pit 23.

FIG. 9 is a perspective view of the sewage tank 10 with wall panels 25mounted around the perimeter of the tank floor 11.

FIG. 10 is a front cross-sectional view along line 10-10 of FIG. 9showing a channel 43 extending from the third section 17 for mountingwall panel 25 with a third gasket 47.

FIG. 11 is a cross-sectional view along line 11-11 of FIG. 9 showing atongue 25h and a groove 25i in adjoining wall panels 25 withintermediate gasket 48 for sealing and locking the wall panels 25together.

GENERAL DESCRIPTION

The present invention relates to a sewage collection and separation tankfor density separation of sewage which prevents leakage of the sewagefrom the tank which comprises: a preformed concrete sump box meansadapted to be recessed in a floor of an earthen pit and at least onesidewall extending from the bottom wall around a vertical axis, the sumpbox means having a first gasket means mounted in an outer surface of thesidewall and spaced above the bottom wall of the sump box means; apoured concrete tank floor on the floor of the earthen pit around theouter surface of the sump box means which envelopes the first gasketmeans of the sump box means, wherein the tank floor has been poured inconsecutive sections radially around the vertical axis and the outersurface of the sidewall of the sump box means, each section having alower face adjacent to the floor of the pit and a spaced apart upperface and spaced apart first and second sides between the faces andspaced apart edges between the sides; a second gasket means extendinglaterally from the first gasket means mounted in the sidewall of thesump box means, the second gasket means mounted along a first side of afirst section of the tank floor so that when a last section of the tankfloor is poured, a second side of the last section and the first side ofthe first section envelope the second gasket means to form a sealbetween the last section and the first section; and a tank wallextending from the tank floor to define the tank.

Furthermore, the present invention relates to a precast concretestructure for a sewage collection and separation tank for densityseparation of sewage which prevents leakage of the sewage from the tankand which is adapted to be recessed in a floor of an earthen pit whichcomprises: a preformed concrete sump box means adapted to be recessed ina floor of an earthen pit with a bottom wall and at least one sidewallextending from the bottom wall around a vertical axis; and a firstgasket means mounted in an outer surface of the sidewall of the sump boxmeans and spaced above the bottom wall of the sump box means.

The precast invention relates to a method for constructing a sewagecollection and separation tank for density separation of sewage whichprevents leakage of sewage from the tank which comprises: providing apreformed concrete sump box means adapted to be recessed in a floor ofan earthen pit and with a bottom wall and at least one sidewallextending from the bottom wall around a vertical axis, the sump boxmeans having a first gasket means mounted in an outer surface of thesidewall and spaced above the bottom wall of the sump box means;mounting the sump box means in the earthen pit; pouring a concrete tankfloor on the floor of the earthen pit around the outer surface of thesump box means which envelopes the first gasket means of the sump boxmeans, wherein the tank floor is poured in consecutive sections radiallyaround the vertical axis and the outer surface of the sidewall of thesump box means, each section having a lower face adjacent to the floorof the pit and a spaced apart upper face and spaced apart first andsecond sides between the faces and spaced apart edges between the sidesand wherein a second gasket means that extends laterally from the firstgasket means is mounted in the sidewall of the sump box means along afirst side of a first section of the tank floor so that when a lastsection of the tank floor is poured, a second side of the last sectionand the first side of the first section envelope the second gasket meansto form a seal between the last section and the first section; mountingpreformed tank walls around the concrete floor to produce the tank.

The grooves which provide for mounting the elastomeric gaskets aremulti-sided and preferably semi-hexagonal. A multi-sided groove providesa tortuous path that a liquid will have to travel to leak between thegasket and the groove. The more tortuous the path, the greater thelikelihood that a liquid impervious seal will be formed between thegasket and the groove. It is also important that the gasket sealproperly in the multi-sided groove to provide the liquid imperviousseal.

SPECIFIC DESCRIPTION

The preferred embodiment of a sewage collection and separation tank 10of the present invention and method for constructing the sewage tank 10is shown in FIGS. 1 to 11. The sewage tank 10 (FIG. 9) is comprised of aconcrete sewage tank floor 11 formed from four poured concrete sections13, 15, 17 and 19 poured on a graded earthen site 21 around a sump pumppit 23 (FIG. 8). Sidewalls consisting of interlocking wall panels 25extend from an outer periphery of the tank floor 11.

Referring specifically to FIGS. 7 and 8, the earthen site 21 where thesewage tank 10 is to be constructed is first surveyed, staked and thengraded. A sump pump pit excavation 27 for the sump pump pit 23 is thendug. The excavation 27 has a square cross-section along the verticalaxis and is dug slightly larger than the sump pump pit 23 which will bemounted in the sump pump pit excavation 27.

Before the sewage tank floor 11 is poured, rectangular footing holes ordepressions 29 are dug in the earthen site 21 and an earthen shoulder 31is contoured around the perimeter of the earthen site 21. The footingholes 29 have a square shape along a vertical axis. Although five rowsof six footing holes 29 are preferred, any number of rows of footingholes or any pattern of footing holes 29 can be used depending on theareal extent of the sewage tank floor 11. The primary function of thefooting holes 29 and the shoulder 31 is to provide stability for thesewage tank floor 11. A plurality of metal reinforcing rods 33 aredriven vertically into the shoulder 31. The rods 33 support a removeablemolding or form member (not shown) that provides a main channel 43 formounting the wall panels 25 (FIGS. 8 and 10).

Once the earthen site 21 has been prepared, the sump pump pit 23 ismounted in the sump pump pit excavation 27. As shown in FIGS. 6 and 8,the sump pump pit 23 is a unitary concrete box having spaced apartsidewalls 23a and 23b extending from a bottom wall 23c with end walls23d and 23e between the sidewalls 23a and 23b. The sump pump pit 23 hasa square cross-section when viewed along the vertical axis a--a.

A semi-hexagonal groove 35 is preformed or cut in the outside of thesidewalls 23a and 23b, and in the outside of the end walls 23d and 23eof the sump pump pit 23, spaced from the upper ends 23f and 23g of thesidewalls 23a and 23b and the upper ends 23h and 23i of the end walls23d and 23e. The distance of the semi-hexagonal groove 35 from the upperends 23f and 23g of the sidewalls 23a and 23b and from the upper ends23h and 23i of the end walls 23d and 23e is preferably one-half thethickness of the sewage tank floor 11. A first hexagonal elastomericgasket 37, preferably made of rubber, is then mounted in the groove 35.The first gasket 37 has a length sufficient to extend the length of theperimeter of the sump pump pit 23 and can be overlapped or solventwelded together between abutting ends.

After the sump pump pit 23 has been mounted in the excavation 27, thesewage tank floor 11 of the sewage tank 10 is constructed. As shown insequence in FIGS. 1 to 4, a first section 13, having a cuneiform orwedge shape (FIG. 1), is poured extending from the sidewall 23a of thesump pump pit 23 to the shoulder 31 of the earthen site 21. The firstsection 13 is comprised of an upper face 13a that extends from the upperend 23f of the sidewall 23a of the sump pump pit 23 and a lower face 13bpoured against the earthen site 21, essentially parallel to the uppersurface 13a (FIG. 6), with spaced apart sides 13c and 13d between thefaces 13a and 13b, and edges 13e and 13f between the sides 13c and 13d.The first section 13 has a thickness that is sufficient to encase thefirst gasket 37 at an intermediate position between the upper face 13aand the bottom face 13b of the first section 13. This provides a liquidtight seal between the side 23a of the sump pump pit 23 and the frontedge 13e of the first section 23.

As shown in FIG. 5, a semi-hexagonal groove 39 is provided in side 13cby a molding or form member (not shown). The groove 39 extends theentire length of the side 13c from the first gasket 37 mounted in theside 23a of the sump pump pit 23 to the back edge 13f of the firstsection 13 adjacent to the shoulder 31 of the earthen site 21. Prior topouring the final section 19, a second elastomeric hexagonal gasket 41is then mounted in the groove 39 with one end (not shown) abuttingagainst the first gasket 37 mounted in the side 23a of the sump pump pit23. This provides a liquid tight seal between the sump pump pit 23 andthe front edge 13e of the first section 13. The second gasket 41 extendsthe entire length of the groove 39 along the side 13c of the firstsection 13.

After the upper face 13a of the first section 13 has been screed to asmooth surface and while the side 13d is still wet, the second section15 is poured as shown in FIG. 2. The second section 15 of the sewagetank floor 11 is similar to the first section 13 and extends from theend wall 23d of the sump pump pit 23 to the shoulder 31 of the earthensite 21. The second section 15 is comprised of an upper face 15a and aparallel lower face 15b with spaced apart sides 15c and 15d between thefaces 15a and 15b and edges 15e and 15f between the sides 15c and 15d.Side 15c abuts against the side 13d of the first section 13. Since thetwo sides 13d and 15c are comprised of wet cement, a large unitary areaconsisting of sections 13 and 15 is formed that is impervious toliquids. In a similar manner as edge 13e of section 13 encased the firstgasket 37 mounted on the side 23a of the sump pump pit 23, the frontedge 15e of the second section 15 encases that part of the first gasket37 mounted along the end 23d of the sump pump pit 23. This forms aliquid impervious seal between the second section 15 and the end 23d ofthe sump pump pit 23.

After the upper face 15a of the second section 15 of the sewage tankfloor 11 has been screed to a smooth surface, and while the concrete atthe side 15d is still wet, concrete for the third section 17 is pouredas shown in FIG. 3. The third section 17 of the sewage tank floor 11extends from the side 23b of the sump pump pit 23 to the shoulder 31 ofthe earthen site 21. The third section 17 is comprised of an upper face17a and a parallel lower face 17b with spaced apart sides 17c and 17dbetween the faces 17a and 17b, and edges 17e and 17f between the sides17c and 17d. Side 17c abuts against the side 15d of the second section15. Since the two sides 17c and 15d are comprised of wet cement, thesewage tank floor 11 is extended so that sections 13, 15 and 17 form aunitary area that is impervious to liquid seepage into the earthen site21 below. The front edge 17e of the third section 17 encases that partof the first gasket 37 mounted along the side 23b of the sump pump pit23. This forms a liquid impervious seal between the third section 17 andthe sump pump pit 23.

Once the upper face 17a of the third section 17 has been screed to asmooth surface, the sewage tank floor 11 is ready to be completed. Thefourth and final section 19 extends from the end 23e of the sump pumppit 23 to the shoulder 31 of the earthen site 21 and is shown in FIG. 4.The fourth section 19 is comprised of an upper face 19a and a parallellower face 19b with spaced apart sides 19c and 19d between the faces 19aand 19b, and edges 19e and 19f between the sides 19c and 19d. Side 19cabuts against the side 17d of the third section 17 while the side 19dabuts against the side 13c of the first section 13. The front edge 19eof the fourth section 19 encases that part of the first gasket 37mounted along the end 23e of the sump pump pit 23. Since the side 17d ofthe third section 17 and the side 19c of the fourth section 19 arecomprised of wet cement, the third and fourth sections 17 and 19 form aunitary area extending around the perimeter of the sump pump pit 23.However, by the time that the fourth section 19 is poured, the side 13cof the first section 13 has dried. It is extremely difficult to bond wetcement to dry cement to create a liquid impervious seal between the twocements.

Before the fourth section 19 is poured, half of the second gasket 41,mounted in the groove 39 along the side 13c of the first section 13, isexposed. When the fourth section 19 is poured, the side 19d of thefourth section 19 encases the second gasket 41 and forms a liquidimpervious seal along the seam between the first and fourth sections 13and 19. Thus, the first gasket 37 seals along all the seams between thefour sections 13, 15, 17 and 19 and the sump pump pit 23 while thesecond gasket 41 seals along the seam between the first section 13 andthe fourth section 19. The two gaskets 37 and 41 act as sealing membersfor the sewage tank 10 whenever there is a wet concrete member beingpoured abutting against a dry concrete member.

The sewage collection and separation tank 10 is completed by wall panels25. As the sections 13, 15, 17 and 19 of the tank floor 11 are poured,the earthen shoulder 31 is encased in concrete while the rods 33 supporta removeable form (not shown) that serves to shape the main channel 43around the perimeter of the tank floor 11 for mounting the wall panels25 (FIGS. 8 and 10). As shown in cross-section in FIGS. 8 and 10,reinforcing rods 44 are laid horizontally, adjacent to the rods 33. Thereinforcing rods 44 are fastened to the rods 33 by fasteners (not shown)or welding and add support to the rods 33 supporting the removeable formor mold for the main channel 43. A semi-hexagonal groove 45 is providedinside the main channel 43 by the molding or form member (not shown) andserves for mounting a third hexagonal gasket 47. The third hexagonalgasket 47 is preferably made of rubber and is mounted in the groove 45with half of the gasket 47 remaining exposed.

The third gasket 47 abuts against the second gasket 41 mounted betweensections 13 and 19 of the tank floor 11 and provides a liquid imperviousseal between the wall panels 25 and the tank floor 11. The wall panels25 are preformed concrete with spaced apart front and back sides 25a and25b with ends 25c and 25d between the sides 25a and 25b and edges 25eand 25f between the ends 25c and 25d. The bottom end 25c of each wallpanel 25 is provided with a semi-hexagonal groove 25g (FIG. 10) whilethe edge 25e has a tongue 25h and edge 25f has a groove 25i (FIG. 11).

As shown in FIG. 10, the wall panels 25 are mounted in the channel 43,standing on end 25c. The groove 25g in the panels 25 encases the thirdgasket 47 to form a liquid impervious seal between the panels 25 and thetank floor 11. The wall panels 25 can also be sealed in the channel 43with a bitumastic coating over a non-shrink grout (not shown) or thewall panels 25 can be sealed in the channel 43 with the third gasket 47in conjunction with the bitumastic coating.

The panels 25 are joined to each other with the tongue 25h of one panel25 mating with the groove 25i of another panel 25 to form a jointbetween side-by-side panels 25. A fourth elastomeric gasket 49,preferably made of rubber, is mounted between the tongue 25h and thegroove 25i of adjoining wall panels 25 to form a liquid impervious sealbetween the side-by-side panels 25 as shown in FIG. 11. The fourthgasket 49 extends to the third gasket 47 and together the third andfourth gaskets 47 and 49 form a liquid impervious seal between the wallpanels 25 and the tank floor 11. A sufficient number of wall panels 25are assembled around the perimeter of the tank floor 11 to completelysurround the tank floor 11. Adjoining wall panels 25 can also be sealedto each other by a bitumastic coating over a non-shrink grout (notshown) or the fourth gasket 49 can be used in conjunction with thebitumastic coating. The wall panels 25 can be further supported bybackfill (not shown) from earth excavated to build the earthen site 21.

A pump 51 is inserted in the sump pump pit 23 when the tank 10 isemptied. The pump 51 allow solids that precipitate from sewage held inthe sewage tank 10 to be drawn off and pumped out of the sewage tank 10so that the remaining liquids in the sewage tank 10 can be chemicallytreated for reintroduction back into the environment. The sewagecollection and separation tank 10 is preferably completed by a roof (notshown) formed of a plurality of precast, interlocking roof panels (notshown). The roof panels are preferably supported by columns (not shown)extending from the tank floor 11 to the roof panels.

As can be seen in FIG. 8, the opposed sections 15 and 19 of the sewagetank floor 11 have a slope of between about 3° and 6.5° degrees withrespect to the horizontal form the shoulder 31 to the vertical axisa--a. The sections 13 and 17 have a similar slope. The slope of thesections 13, 15, 17 and 19 helps to funnel solids held in the sewagetank 10 to the sump pump pit 23 where they can be pumped out of the tank10 by the pump 51 for proper disposal.

It should be understood that any number of the preferred tank floors 11can be constructed side-by-side (not shown) to form an enlarged sewagetank area. In this case, wall panels 25 would only be constructed aroundthe outer periphery of the sewage tank 10 proper. Also, the individualsewage tank floors 11 will be sealed to each other by a gasket (notshown) mounted in a groove (not shown) along the common border of theside-by-side tank floors 10 in a similar manner as the second gasket 41is mounted between the first section 13 and the fourth section 19.

Numerous variations will occur to those skilled in the art. It isintended, therefore, that the foregoing descriptions be onlyillustrative of the present invention and that the present invention belimited only by the hereinafter appended claims.

I claim:
 1. A sewage collection and separation tank for densityseparation of sewage which prevents leakage of the sewage from the tankwhich comprises:(a) a preformed concrete sump box means adapted to berecessed in a floor of an earthen pit with a bottom wall and at leastone sidewall extending from the bottom wall around a vertical axis, thesump box means having a first gasket means mounted in an outer surfaceof the sidewall and spaced above the bottom wall of the sump box means;(b) a poured concrete tank floor on the floor of the earthen pit aroundthe outer surface of the sump box means which envelopes the first gasketmeans of the sump box means, wherein the tank floor has been poured inconsecutive sections radially around the vertical axis and the outersurface of the sidewall of the sump box means, each section of the tankfloor having a lower face adjacent to the floor of the pit and a spacedapart upper face and spaced apart first and second sides between thefaces and spaced apart edges between the sides; (c) a second gasketmeans extending laterally from the first gasket means mounted in thesidewall of the sump box means, the second gasket means mounted along afirst side of a first section of the tank floor so that when a lastsection of the tank floor is poured, a second side of the last sectionand the first side of the first section envelope the second gasket meansto form a seal between the last section and the first section; and (d) atank wall extending from the tank floor to define the tank.
 2. Thesewage collection and separation tank of claim 1 wherein the sump boxmeans has a rectangular cross-section perpendicular to the verticalaxis, and wherein the bottom wall of the sump box means is rectangularwith four sidewalls extending from the bottom wall.
 3. The sewagecollection and separation tank of claim 2 wherein the tank floor iscomprised of four sections and wherein the sides of adjacent sectionsabut along a plane that intersects one of the sidewalls of the sump boxmeans.
 4. The sewage collection and separation tank of claim 1 whereinthe first gasket means has spaced apart ends and is mounted in a firstgroove in and around the outer surface of the sidewall of the sump boxmeans so that the ends of the first gasket means abut each other toprovide a seal.
 5. The sewage collection and separation tank of claim 4wherein the first gasket means is made of an elastomer which is mountedin the first groove of the sump box means and wherein the spaced apartends of the first gasket means are solvent bonded or welded togetherwhen the first gasket means is mounted in and around the sump box means.6. The sewage collection and separation tank of claim 3 wherein thesecond gasket means is mounted in a second groove in the first side ofthe first section of the tank floor and the second gasket means isenveloped by the second side of the last section of the tank floor. 7.The sewage collection and separation tank of claim 6 wherein the secondgasket means is made of an elastomer.
 8. The sewage collection andseparation tank of claim 1 wherein a pump means is mounted in the sumpbox means and provides for removal of accumulated solids in the sump boxmeans.
 9. The sewage collection and separation tank of claim 1 whereinthe upper face of the sections of the tank floor incline downwardly andinwardly from an outer edge of the earthen pit to the sump box means atan angle of between 3° and 6.5° degrees from a horizontal plane.
 10. Thesewage collection and separation tank of claim 1 wherein the tank floorhas a rectangular shape perpendicular to the vertical axis.
 11. Thesewage collection and separation tank of claim 1 wherein footings areprovided in the earthen pit to support the sections of the concrete tankfloor.
 12. The sewage collection and separation tank of claim 7 whereinthe tank wall is comprised of a plurality of preformed concrete wallpanels extending around the tank floor and having spaced apart front andback sides with spaced apart top and bottom ends between the sides andspaced apart first and second edges between the ends, wherein thesections of the tank floor are provided with a third groove formedaround the tank floor, the third groove mounting a third gasket meansabutting against the second gasket means mounted between the firstsection and the last section of the tank floor, the third gasket meansmating with a groove provided in the bottom end of the wall panels toprovide a seal between the wall panels and the tank floor and whereinadjacent wall panels are provided with a locking joint means to lock andseal the adjacent wall panels together.
 13. The sewage collection andseparation tank of claim 12 wherein the locking joint means for theadjacent wall panels is a tongue and a groove provided in adjacent firstand second edges of the adjacent wall panels with a fourth gasket meansprovided between the locking joint means to seal the adjacent wallpanels.
 14. The sewage collection and separation tank of claim 13wherein there are a plurality of poured concrete tank floors poured onthe floor of the earthen pit around the outer surface of respective sumpbox means, wherein adjoining tank floors are poured side-by-side with afifth gasket means mounted in a fourth groove formed in an outer edge ofone of the sections of the first tank floor which abuts against an outeredge of one of the sections of the adjoining tank floor, wherein whenthe one of the sections of the adjoining tank floor is poured, the fifthgasket means mounted in the fourth groove in the outer edge of the oneof the sections of the first tank floor is enveloped by the outer edgeof the one of the sections of the first tank floor and the outer edge ofthe one of the sections of the adjoining tank floor to provide a liquidimpervious seal between adjoining tank floors and wherein the tank wallextends from the plurality of tank floors to define the tank.
 15. Thesewage collection and separation tank of claim 14 wherein the first,second, third, fourth and fifth gasket means are mounted in multi-sidedgrooves.
 16. The sewage collection and separation tank of claim 15wherein the multi-sided grooves are semi-hexagonal.
 17. The sewagecollection and separation tank of claim 13 wherein an end of the fourthgasket means abuts against the third gasket means mounted around thetank floor for providing a liquid impervious seal between the wallpanels and the tank floor.
 18. The sewage collection and separation tankof claim 12 wherein the sections of the tank floor are provided with achannel which provides for the third groove formed around the tank floorand which provides for mounting the wall panels in the channel.
 19. Thesewage collection and separation tank of claim 1 wherein earth removedto form the earthen pit is used as backfill to support the tank wallextending from the tank floor.
 20. The sewage collection and separationtank of claim 14 wherein the third the fourth and the fifth gasket meansare made of an elastomer.
 21. The sewage collection and separation tankof claim 13 wherein the third and the fourth gasket means are made of abitumastic compound.
 22. A method for constructing a sewage collectionand separation tank for density separation of sewage which preventsleakage of sewage from the tank which comprises:(a) providing apreformed concrete sump box means adapted to be recessed in a floor ofan earthen pit and with a bottom wall and at least one sidewallextending from the bottom wall around a vertical axis, the sump boxmeans having a first gasket means mounted in an outer surface of thesidewall and spaced above the bottom wall of the sump box means; (b)mounting the sump box means in the earthen pit; (c) pouring a concretetank floor on the floor of the earthen pit around the outer surface ofthe sump box means which envelopes the first gasket means of the sumpbox means, wherein the tank floor is poured in consecutive sectionsradially around the vertical axis and the outer surface of the sidewallof the sump box means, each section having a lower face adjacent to thefloor of the pit and a spaced apart upper face and spaced apart firstand second sides between the faces and spaced apart edges between thesides and wherein a second gasket means that extends laterally from thefirst gasket means is mounted in the sidewall of the sump box meansalong a first side of a first section of the tank floor so that when alast section of the tank floor is poured, a second side of the lastsection and the first side of the first section envelope the secondgasket means to form a seal between the last section and the firstsection; and (d) mounting preformed tank walls around the concrete floorto produce the tank.
 23. The method of constructing the sewagecollection and separation tank of claim 22 wherein the sump box meanshas a rectangular cross-section when viewed along the vertical axis, andwherein the bottom wall of the sump box means is rectangular with foursidewalls extending from the bottom wall.
 24. The method of constructingthe sewage collection and separation tank of claim 23 wherein the tankfloor is poured with four sections and wherein the sides of adjacentsections abut along a plane that intersects one of the sidewalls of thesump box means.
 25. The method of constructing the sewage collection andseparation tank of claim 22 wherein the first gasket means has spacedapart ends and is mounted in a first groove in and around the outersurface of the sidewall of the sump box means so that the ends of thefirst gasket means abut each other.
 26. The method of constructing thesewage collection and separation tank of claim 25 wherein the firstgasket means is made of an elastomer which is mounted in the firstgroove of the sump box means and wherein the spaced apart ends of thefirst gasket means are overlapped when the first gasket means is mountedin and around the sump box means.
 27. The method of constructing thesewage collection and separation tank of claim 24 wherein the secondgasket means is mounted in a second groove in the first side of thefirst section of the tank floor and the second gasket means is envelopedby the second side of the last section of the tank floor.
 28. The methodof constructing the sewage collection and separation tank of claim 24wherein the second gasket means is made of an elastomer.
 29. The methodof constructing the sewage collection and separation tank of claim 22wherein a pump means is mounted in the sump box means and provides forremoval of accumulated solids in the sump box means.
 30. The method ofconstructing the sewage collection and separation tank of claim 22wherein the sections of the tank floor are poured with an upper facewhich inclines downwardly and inwardly from an outer edge of the earthenpit to the sump box means at an angle of between 3° and 6.5° degreesfrom a horizontal plane.
 31. The method of constructing the sewagecollection and separation tank of claim 22 wherein the tank floor ispoured to have a rectangular shape when viewed along the vertical axis.32. The method of constructing the sewage collection and separation tankof claim 22 wherein footings are dug in the earthen pit to support thesections of the concrete tank floor.
 33. The method of constructing thesewage collection and separation tank of claim 22 wherein the tank wallis provided by mounting a plurality of preformed concrete wall panelsaround the tank floor, the panels each having spaced apart front andback sides with spaced apart top and bottom ends between the sides andspaced apart first and second edges between the ends, wherein thesections of the tank floor are provided with a third groove formedaround the tank floor, the third groove mounting a third gasket meansabutting against the second gasket means mounted between the firstsection and the last section of the tank floor, the third gasket meansmating with a groove provided in the bottom end of the wall panels toprovide a seal between the wall panels and the tank floor and whereinadjacent wall panels are provided with a locking joint means to lock theadjacent wall panels together.
 34. The method of constructing the sewagecollection and separation tank of claim 33 wherein the locking jointmeans for the adjacent wall panels is a tongue and a groove which aremounted in adjacent first and second edges of the adjacent wall panelswith a fourth gasket means provided between the locking joint means toseal the adjacent wall panels.
 35. The method of constructing the sewagecollection and separation tank of claim 34 wherein there are a pluralityof poured concrete tank floors poured on the floor of the earthen pitaround the outer surface of respective sump box means, wherein adjoiningtank floors are poured side-by-side with a fifth gasket means mounted ina fourth groove formed in an outer edge of one of the sections of thefirst tank floor that abuts against an outer edge of one of the sectionsof the adjoining tank floor, wherein when the one of the sections of theadjoining tank floor is poured, the fifth gasket means mounted in thefourth groove in the outer edge of the one of the sections of the firsttank floor is enveloped by the outer edge of the one of the sections ofthe first tank floor and the outer edge of the one of the sections ofthe adjoining tank floor to provide a liquid impervious seal betweenadjoining tank floors and wherein the tank wall extends from theplurality of tank floors to define the tank.
 36. The method ofconstructing the sewage collection and separation tank of claim 35wherein the first, second, third, fourth and fifth gasket means aremounted in multi-sided grooves.
 37. The method of constructing thesewage collection and separation tank of claim 36 wherein themulti-sided grooves are semi-hexagonal.
 38. The method of constructingthe sewage collection and separation tank of claim 34 wherein an end ofthe fourth gasket means is abutted against the third gasket meansmounted around the tank floor for providing a liquid impervious sealbetween the wall panels and the tank floor.
 39. The method ofconstructing the sewage collection and separation tank of claim 33wherein the sections of the tank floor are provided with a channel whichprovides for the third groove formed around the tank floor and whichprovides for mounting the wall panels in the channel.
 40. The method ofconstructing the sewage collection and separation tank of claim 22wherein earth removed to form the earthen pit is used as backfill tosupport the tank wall extending from the tank floor.
 41. The method ofconstructing the sewage collection and separation tank of claim 35wherein the third the fourth and the fifth gasket means are made of anelastomer.
 42. The method of constructing the sewage collection andseparation tank of claim 34 wherein the third and the fourth gasketmeans are made of a bitumastic compound.